President Donald Trump's proposal to build a sunshine-powered wall bordering Mexico, trotted out in public for the first time this week, strikes solar experts as kinda nuts.

"Putting solar panels on a stupid wall does not change the fact that the wall is a stupid and pointless waste of money," geoscientist Raymond Pierrehumbert of the University of Oxford in the UK told BuzzFeed News by email.

Trump was elected promising to "build a wall" with Mexico, anywhere from 200 to 1,000 miles long, depending on the speech, and costing perhaps $67 billion. Screwing solar panels onto this wall would add $1.4 to $4.2 billion to that cost, according to one preliminary industry estimate, with the solar panels possibly generating more than $100 million of electricity every year.

“We’re thinking about building the wall as a solar wall, so it creates energy and pays for itself," Trump said at an Iowa rally on Wednesday night, suggesting that Mexico would buy this border electricity. Mexican President Enrique Peña Nieto has resolutely opposed having anything to do with Trump's wall. Former Mexican president Vincente Fox has been even more scathing:

The Trump administration has already loosened environmental rules to help the domestic coal, oil, and gas industries, such as rescinding Obama’s climate action plan and halting rules to reduce methane emissions from oil and gas wells on public lands — all while remaining relatively quiet on renewables.

Energy policy experts say Trump’s pitch to cover a border wall with solar panels is technically feasible, probably. But it wouldn’t be easy, they say, and makes little economic sense.

“While perhaps technologically feasible, there are many more technical and cost considerations than just slapping a bunch of solar panels onto the wall, including how that electricity is utilized and routed,” MJ Shiao, who leads the research analyst team at GTM research, wrote in an email to BuzzFeed News. “We believe there are more fiscally effective policies and avenues to deploy large amounts of solar than on an unpopular border wall.”

It’s hard to overstate the scale of Trump’s proposed solar wall: It would dwarf all other solar facilities, multiplying US solar output by about 50 times. Even at 40 feet tall (the lower end of Trump’s hypothetical height range of 35 to 65 feet), the wall would require more than twice as much concrete to build as the Hoover Dam, according to a November estimate.

With any major energy infrastructure project, the more complexity, the harder and more expensive it is to make work, Shiao said. This project would likely face a messy web of permits and other regulations because of crossing state and country lines, leaving aside the reality that sitting solar panels atop a giant wall, or lining the sides of it, aren’t necessarily the best way to maximize solar output.

If it made sense to mount solar panels on long linear walls, energy companies would do that already, Pierrehumbert said. Instead they mostly put solar panels on the ground in farms where they minimize ecological damage and cost less to maintain.

What’s more, a solar energy installation that passes through multiple states and jurisdictions will face "challenging" permit requirements, Brian Lips of the NC Clean Energy Technology Center told BuzzFeed News. Plus, the wall would likely need a lot of infrastructure, such as transmission lines, to connect the wall’s solar power to market.

Economically, it would make more sense to hire people in Mexico to plant solar panels there, Pierrehumbert added, both to save on labor costs and dissuade immigration. This idea was proposed last year by Mexican academics. (Illegal immigration from Mexico actually peaked in 2000, and has been declining since the 2008 recession.)

But one firm, Gleason Partners LLC of Las Vegas, has bid to attach solar panels to the border wall.

"If the price is right, I’m sure you can get solar companies to do anything," Lips said.